<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        body,html{
            width: 100%;
            height: 100%;
            background-color: gray;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        .box{
            position: relative;
            width: 500px;
            height: 500px;
            display: flex;
            align-items: center;
            justify-content: center;
        }
        .box span{
            background-color: steelblue;
            position: absolute;

            border-radius: 50%;
            animation: animation 3s linear infinite none;
            animation-delay: calc(0.5s * var(--i));
        }
        @keyframes animation {
            0%{
                width: 0;
                height: 0;
                opacity: 1;
            }
            50%{
                opacity: 1;
            }
            100%{
                width: 100%;
                height: 100%;
                opacity: 0;
            }
        }
    </style>
</head>
<body>
    <div class="box">
        <span style="--i:1"></span>
        <span style="--i:2"></span>
        <span style="--i:3"></span>
        <span style="--i:4"></span>
        <span style="--i:5"></span>
        <span style="--i:6"></span>
        <span style="--i:7"></span>
    </div>
</body>
</html>